Incomplete Dominance: A type of
intermediate inheritance
• Neither original allele of a gene dominates
alone.
• Inherited alleles share dominance.
• The alleles are “blended,” to show a mix
between the two.
– Ex: Make your own.
Polygenic
• A form of inheritance.
• Two or more genes (Poly) affect one
characteristic of an organism.
• Ex: There are multiple genes for height in
humans.
– Humans inherit three alleles for height from three
separate height genes from each parent.
– Someone inherits only tall alleles from their father
and only short alleles from their mother.
– Alleles of are expressed as incomplete dominance,
this person’s height is a mix or blend of all height
alleles.
Codominance
• Neither original allele of a gene dominates
alone.
• Inherited alleles share dominance.
• The alleles remain separate and are both
expressed as individuals.
– Ex: Make your own.
Multiple Alleles
• Genes may have more than two alleles
possible. Ex. Natural hair color.
• A person can only inherit two alleles for a gene,
unless some mutation occurs during meiosis.
– Ex.: Mom has alleles for black and brown hair.
Dad has alleles for red and blonde hair. Offspring
may inherit the black allele from mom and the
blonde allele from dad.
• Multiple alleles provides diversity in a
population of organisms like humans.
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Principle of Segregation
• Proposed theory by Mendel from his
experiments with simple plant cross-breeding.
• During Meiosis of sex cells:
– Inherited chromosomes with genes (characters)
and specific alleles (traits) from parents are
separated into gametes (sperm or egg cells).
– Each gamete produced carries only one allele of
each gene on an individual chromosome.
– Ex: One sperm cell may carry the eye color brown
while a different sperm cell may carry green eye
color.
Principle of Independent Assortment
• Proposed theory by Mendel from his
experiments with simple plant cross-breeding.
• During Meiosis of sex cells:
– Any allele can be sorted to any sex cell.
– Any allele of a gene can be sorted with any allele
from a different gene.
– There is a random assortment of independent
alleles in each sex cell.
– This adds to the diversity of characteristics within a
population of organisms.
Sex-Linked Genes
• Any gene that only occurs on a sex
chromosome, a chromosome which determines
the sex of an organism (male or female).
• A sex-linked gene will be only associated with
one of the sex-chromosomes, male or female.
• This can be useful for tracking genetic disorders
in families.
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